It is apparent to all that waste materials from homes, businesses, manufacturing operations, etc. are being produced in larger and larger amounts and thereby are causing disposal problems which are becoming increasing difficult to solve. Atmospheric pollution results from attempts to burn such waste materials to reduce its volume to that of ashes. The only other viable solution is to recycle these waste materials to be used over and over again in the production of new products. While recycling is a popular and deserving solution, it is often extremely difficult to separate one type of material from another in order to concentrate any particular material for recycling. Furthermore, many of such waste products are so small in size that the separation problems assume such gigantic proportions that they appear to be completely impractical.
The use of electric energy in separation processes has been employed many times in the past, e.g. in electostatic separators for dust particles and such small sized materials. In some types of separation procedures particles are given an electric charge and then attracted to a surface of the opposite electric charge and removed from that surface. Other electrical methods of separation are well known to the skilled engineers in this field.
Another development employs a nonuniform electric field to act upon certain neutral particles causing those particles to move toward the location where the electric field has its highest intensity. This phenomenon is called dielectrophoresis. When neutral particles having suitable dielectric, dipole moment or shape differences are subjected to a nonuniform electric field they become polarized, frequently referred to as "dipoles", having an equal amount of plus and minus charges each concentrated on opposite sides of the particle, which causes the particle to become oriented so that its plus charges are attracted to the minus electrode and its minus charges are attracted to the plus electrode. Such a particle in a uniform electric field will not move in any direction because the forces acting upon it are balanced. In a nonuniform electric field, however, an analysis of the forces acting upon the particle shows that the particle will tend to move toward the location of highest field intensity. For example, in a field developed between a small sphere and a flat plate the location of highest field intensity is at the surface of the sphere and accordingly the particles will move toward the sphere. A detailed explanation of this phenomenon can be found in "ELECTROSTATIC AND IT'S APPLICATION", Wiley-Interscience, 1973, Chapter 14.
The principle of dielectophoresis has been employed in U.S. Pat. No. 3,162,592 to H. A. Pohl in describing a method and apparatus for separating materials by subjecting them to a nonuniform electric field. In this patent a mixture of particles, e. g. rutile and polyvinylchloride are introduced to an inclined trough over which is positioned an arcuate electrode. Under the trough is a uniform metal plate serving as an electrode and a field is generated between the curved electrode above the trough and the metal plate below the trough. This field is nonuniform because of the shape of the curved electrode above the trough and it acts upon the mixture of particles sliding down the inclined trough. By the time the particles reach the end of the trough the field has acted upon the particles and caused a significant separation in which the rutile particles are deflected by the electric field and the polyvinylchloride particles are substantially unaffected by the electric field. The entire zone of the electric field in this patent takes place in a dielectric liquid such as benzene.
It is an object of this invention to provide a novel apparatus and method for separating materials by dielectrophoresis.
It is another object of this invention to provide a separation process where the nonuniform electric field is produced in a medium of air. It is another object of this invention to provide a nonuniform electric field between a rotating convex surface and a flat surface to provide an improved separation process.
It is still another object of this invention to provide a continuous separation process whereby a conical electrode is rotated and continuously cleaned of any particles clinging to the surface which might adversely affect the functioning of the separation process.
Still other objects will appear from the more detailed description of this invention which follows.